1,134 research outputs found
Massive Non-Orthogonal Multiple Access for Cellular IoT: Potentials and Limitations
The Internet of Things (IoT) promises ubiquitous connectivity of everything
everywhere, which represents the biggest technology trend in the years to come.
It is expected that by 2020 over 25 billion devices will be connected to
cellular networks; far beyond the number of devices in current wireless
networks. Machine-to-Machine (M2M) communications aims at providing the
communication infrastructure for enabling IoT by facilitating the billions of
multi-role devices to communicate with each other and with the underlying data
transport infrastructure without, or with little, human intervention. Providing
this infrastructure will require a dramatic shift from the current protocols
mostly designed for human-to-human (H2H) applications. This article reviews
recent 3GPP solutions for enabling massive cellular IoT and investigates the
random access strategies for M2M communications, which shows that cellular
networks must evolve to handle the new ways in which devices will connect and
communicate with the system. A massive non-orthogonal multiple access (NOMA)
technique is then presented as a promising solution to support a massive number
of IoT devices in cellular networks, where we also identify its practical
challenges and future research directions.Comment: To appear in IEEE Communications Magazin
Complexity-Aware Scheduling for an LDPC Encoded C-RAN Uplink
Centralized Radio Access Network (C-RAN) is a new paradigm for wireless
networks that centralizes the signal processing in a computing cloud, allowing
commodity computational resources to be pooled. While C-RAN improves
utilization and efficiency, the computational load occasionally exceeds the
available resources, creating a computational outage. This paper provides a
mathematical characterization of the computational outage probability for
low-density parity check (LDPC) codes, a common class of error-correcting
codes. For tractability, a binary erasures channel is assumed. Using the
concept of density evolution, the computational demand is determined for a
given ensemble of codes as a function of the erasure probability. The analysis
reveals a trade-off: aggressively signaling at a high rate stresses the
computing pool, while conservatively backing-off the rate can avoid
computational outages. Motivated by this trade-off, an effective
computationally aware scheduling algorithm is developed that balances demands
for high throughput and low outage rates.Comment: Conference on Information Sciences and Systems (CISS) 2017, to appea
Initial synchronisation of wideband and UWB direct sequence systems: single- and multiple-antenna aided solutions
This survey guides the reader through the open literature on the principle of initial synchronisation in single-antenna-assisted single- and multi-carrier Code Division Multiple Access (CDMA) as well as Direct Sequence-Ultra WideBand (DS-UWB) systems, with special emphasis on the DownLink (DL). There is a paucity of up-to-date surveys and review articles on initial synchronization solutions for MIMO-aided and cooperative systems - even though there is a plethora of papers on both MIMOs and on cooperative systems, which assume perfect synchronization. Hence this paper aims to ?ll the related gap in the literature
Exploiting Capture Effect in Frameless ALOHA for Massive Wireless Random Access
The analogies between successive interference cancellation (SIC) in slotted
ALOHA framework and iterative belief-propagation erasure-decoding, established
recently, enabled the application of the erasure-coding theory and tools to
design random access schemes. This approach leads to throughput substantially
higher than the one offered by the traditional slotted ALOHA. In the simplest
setting, SIC progresses when a successful decoding occurs for a single user
transmission. In this paper we consider a more general setting of a channel
with capture and explore how such physical model affects the design of the
coded random access protocol. Specifically, we assess the impact of capture
effect in Rayleigh fading scenario on the design of SIC-enabled slotted ALOHA
schemes. We provide analytical treatment of frameless ALOHA, which is a special
case of SIC-enabled ALOHA scheme. We demonstrate both through analytical and
simulation results that the capture effect can be very beneficial in terms of
achieved throughput.Comment: Accepted for presentation at IEEE WCNC'14 Track 2 (MAC and
Cross-Layer Design
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